Against the goblin deck in challenge mode, the AI kept attacking me with goblins even though I had
Collective Restraint and 3 types of basic lands and The Tabernacle of Pendrell Vale and he had insufficient mana. It was also playing more goblins even though he couldn't afford the mana costs to do so.
I did not encounter this problem against any of the other decks in challenge mode, or any other deck at any time. Due to the combat hacks that
Collective Restraint and
Propaganda are using, I wonder if maybe those somehow got skipped due to some card conflict in the goblin challenge deck, like
Goblin Lackey, which he cast on turn 1.
I'll try again and see what happens. This deck easily beat every deck up to that point, and would have beat Goblins, too, except for that.
EDIT: I found the problem.
Goblin Lackey's ability triggers when he tries to attack but fails due to
Propaganda/Collective restraint, and that was how he played free goblins. Then all goblins played with goblin lackey will later be unaffected by those enchantments for some reason. That's the pattern; why I don't know.
EDIT #2: On the last turn, all the goblins attacked me (5 of them) which should have cost 10 mana (1 propaganda) and he had 1 mana left after paying for Tabernacle. Why this should be I don't know.